Every time an electrical heater, lamp or motor is turned on or off, using a single or multiphase switch, relay or contactor, an electrical arc occurs between the two contact points where the single or multiphase power connects to the load. The instantaneous energy contained in the resulting arc is very high (thousands of degrees Fahrenheit). This heat causes the metal molecules in the contact points to travel from the warmer point to the colder point. This metal migration pits out and destroys the contact surfaces over time, eventually leading to equipment failure.
This type of contact failure results in increased maintenance costs, unnecessary down time on production lines, higher frequency of product failures and many other issues that cost companies time, money and reputations. Current solutions in use today address contact arcing with modestly effective devices, including Solid State Relays (SSR's), Hybrid Power Relays (HPR's) which are custom-designed and expensive, and RC snubber circuits, which barely mitigate the problem.
Contact current arc suppression technology is either expensive and short-lived or durable, but risky at the product's end-of-life.
Environmental and health concerns, over the years, have lead to the replacement of highly durable mercury displacement relays (MDR) with electromechanical relays and contactors, leaving both industry and products vulnerable to the negative effects of contact arcing.
There are various undesirable effects of using the current technology, namely, environmental risks associated with disposal, high costs of replacement, and catastrophic end-of-life that needs to be proactively mitigated. Efforts are being made to reduce or eliminate these undesirable behaviors.
Arc Suppressors generally attach across the contact and/or coil terminals of a switch, relay or contactor and require some kind of external power connection or require power from the coil connection.
The two terminal arc suppressor of the present invention extends product life of contacts used today in industry, by many orders of magnitude, typically in excess of 500 times. Its product architecture makes it a generic, low-cost component solution that fits easily into new or existing product design and can be scaled to any type of switch, relay or contactor.
The use of the arc suppressor of the present invention results in increased machinery up-time and dramatic improvements in overall system reliability. It extends switch, relay or contactor life in excess of 500 times, thus resulting in reduced maintenance, repair and replacement costs.
Standard switches, relays or contactors are durable and potentially viable for use for up to 10,000,000 cycles when no load current is flowing. However, these same switches, relays or contactors decay more rapidly when carrying a load current. Their electrical life expectancy is reduced to a fraction of their mechanical life, typically down to 10,000 cycles or less. By comparison, without being subjected to electric currents, standard switches, relays or contactors are as durable as MDR's or SSR's. However, when subjected to electric current, the durability and reliability of these same standard switches, relays or contactors are far lower than environmentally objectionable MDR's unless arc suppressor technology offered by the present invention is added to the configuration.
The inevitable end-of-life (EOL) event for any switch, relay or contactor is failure. Standard switches, relays or contactors either fail closed, open or somewhere in between. But, the EOL failure mode of an MDR is typically catastrophic, with an explosion of its mercury-filled contact chamber and the release of highly toxic mercury vapors into its operating environment. Needless to say, this type of failure is especially undesirable when the MDR is operating in equipment that is used to process or prepare food. To mitigate risk, safety dictates proactive early replacement of these MDR's. The law requires proper disposal of these MDR's, a step often overlooked, to the detriment of the environment. Due to ignorance, equipment containing MDR's is typically buried in landfills that may be close to populated communities.
Industrial and commercial fryers, dryers, heaters, cookers, steamers, rollers, burners, ovens, slicers, dicers, coolers, fridges, freezers commonly utilize MDR's in the food processing industry. Thus, there is a need for arc suppressor-fortified standard switches, relays or contactors so that the mercury-based devices can be eliminated.
Another important dimension of generic switch technology is the use of two components, namely, the relay or contactor coil and its associated contact that may fail occasionally. This is because these components operate in an asynchronous mode. Coil activation generally results in contact closure or opening and this action deploys in a time scale measured in milliseconds. However, coil de-activation may not be as responsive in opening the contact in the same time frame. This is due to micro-welding effects of the pitted-out contact surface landscape. The contact spring force is, sometimes, not strong enough to achieve the separation because of this micro-welding effect. In fact, this issue is accounted for in the relay and contactor manufacturing industry. A less-than-one-second delay in coil de-activation response is not considered a failure. This type of contact failure is reason enough to invalidate the use of the energization status of the relay or contactor coil to assume existence of a suppressible arc in any contact arc suppression solution.
The arc suppressor of the present invention only uses two wires to monitor the contact status and suppress the contact current arc, at the very instant that the contacts transition either from the open-to-close state, or, from the close-to-open state. In doing so, the arc suppressor of the current invention also bridges the gap between the electrical life and the mechanical life of standard switches, relays or contactors. It enables these lower-cost, lower-risk and green standard switches, relays or contactors to achieve the equivalent durability and reliability of MDR's and SSR's.
The arc suppressor of the present invention extends the inevitable EOL of a standard switch, relay or contactor by a factor in excess of 500 times. The arc suppressor to be described herein enables innately environmentally-friendly, low cost, designed standard switches, relays or contactors to be used in applications that these devices could historically not be applied to. Where the industry-standard arc solution was the durable but highly-toxic MDR's or expensive and inefficient, but non-toxic SSR's and HPR's, it can now be standard switches, relays or contactors fortified by a two terminal arc suppressor of the present invention.
Other advantages of the arc suppressor of the present invention include: Two wires only, no cooling required, no need for an external power supply, no neutral connection is required to feed its power supply, it monitors contact status, it suppresses an arc when it occurs and it is only turned on for the duration of one-half period which substantially reduces the fire hazard stemming from having the arc suppressing semiconductor turned on all the time during the contact closed state. When switches, relays or contactors fail, serious fire hazard conditions are often present.
There is a general assumption in the prior art that the coil and contact of a relay or contactor are a somewhat rigidly connected structure which response uniformly to cause and effect. This is not the case. The relay or contactor coil, which in turn activates the relay or contactor contact, is operating in an asynchronous mode. Simply expressed, they appear to not be related to each other, at least on an electronic level. When the coil is being energized by the application of a current through the two associated electromagnetic coil wires and thus forced to a change states from the non-magnetized state to the magnetized state, the relay or contactor contact will not timely respond with a corresponding change in state. In most relay or contactors, there is no guaranteed instance of simultaneity between a relay or contactor coil energization and its associated contact activation. The relationship between a relay or contactor coil and a contact is magnetic and mechanical. Because of the magnetic/mechanical connection, there is a great deal of resulting time lags between the relay or contactor coil change of state and the relay or contactor contact change of state. The time delays between the coil state changes and the contact state changes differ significantly from relay or contactor state-to-relay or contactor state, from time-to-time, from environment-to-environment, from device-to-device, from manufacturer-to-manufacturer, from changes in contact operating current, contact operating voltage and coil operating voltage.
Arcing and resulting micro-welding occur even with most prior art arc suppression approaches.
The only element that determines arc suppression timing is the contact and not the energizing coil of a relay or contactor. Thus the ideal arc suppressor should only require 2 wires for operation, not three, four or more.
Those skilled in the arc recognize that arcing only occurs when the contact transitions from the closed state (make) to the open (break) state. This includes contact bouncing during the transition to the on-state. The arc suppression element in the present invention is only active for not more than 10 ms during the contact transitions. Arc suppression timing is determined by the opening or closing of the contact only. As earlier indicated, arc suppression timing does not depend on the status of the relay or contactor coil.
Appropriate, i.e., timely arc suppression offered by the present invention minimizes thermal and mechanical stresses on the arc suppressor components and thus mitigates the need for cooling. It also minimizes thermal and mechanical stresses on the switch, relay or contactor components and thus mitigates the need for venting. Further, it minimizes the effects of metal migration.
Full arc suppression of mechanical switches, relays or contacts with current state-of-the-art technology is not achievable for mechanical contacts.
Arc suppression is only required for mechanical contacts such as the ones on switches, relays and contactors. It is not required for solid state switches or hybrid power relays; however, those devices are expensive and not universal.
An arc suppressor whose arc suppression element is “always on” during the closed contact state is dangerous. They must be inherently safe and, if not designed correctly, the arc suppressor becomes a fire hazard and a liability.
Arc suppressors of the prior art with three or more wires are neither optimal nor inherently safe because they rely on coil and power to decide when to suppress the arc.
Arc suppressors suppress the arcs generated during switch, relay or contactor transitions when switching lamps, heaters, motors and similar electric loads. Such loads are referred to as resistive, inductive and capacitive loads.
Contact stick times due to the effect of microwelding of 200 ms are common. Even contact stick times of up to 999 ms are deemed acceptable by relay and contactor manufacturers.
Metal migration is the movement of metal alloy material from one contact surface to another. Metal molecules move from the warmer contact point (usually the moving one) to the colder contact point (usually the static one) as the heat of the arc melts the contact alloy material. This micro welding occurs with each contact made under power and increases as the contact surface deteriorates. Only the spring loaded contact armature strength breaks the micro welded contact connection.
Microwelding is due to the arcing that occurs during the transition from contact open to contact close occurring in high current density areas of the contact surface. This effect is also amplified by contact bounce during the transition from the open to the close contact state. The strength of the microweld connection greatly depends on the switch contact surface condition and the strength of the contact arc welding power.